In recent years, wind farms that are composed of a plurality of wind turbine generators and that supply power to a utility grid have become widespread.
Power supplied from such wind farms varies depending on wind conditions. Therefore, output-power limitation, ramp-rate control, reactive-power control, and frequency control are known ways of controlling the wind turbine generators for stabilization in the utility grid.
As described in NPL 1, these controls with respect to the wind turbine generators are realized when a wind farm controller performs a comparison operation for data about the wind turbine generators and measurement data of power, voltage, frequency, power factor, and the like that are supplied from the wind turbine generators to the utility grid, at a connecting point (hereinafter, referred to as “grid connecting point”) between the wind turbine generators constituting the wind farm and the utility grid, and sends various command values to the wind turbine generators.
Data flows between the wind turbine generators and the wind farm controller in a conventional wind farm will be described in more detail with reference to FIG. 9. The upper part of FIG. 9 is an overall diagram, and the lower part of FIG. 9 is a configuration diagram of a conventional wind-turbine control system.
From a higher-level controller 302 provided, for example, in an electric power company, a wind farm controller 300 receives command values Pnet_dem and Qnet_dem that indicate the target values of the amount of active power and the amount of reactive power for the wind farm as a whole. Furthermore, the wind farm controller 300 receives measurement data that indicates the active power, the reactive power, the voltage, and the frequency at the grid connecting point, detected by a data processing and communication processing section 306 included in a substation 310, and receives wind-turbine data about each wind turbine generator 304 via a wind-turbine control system 308 provided for each wind turbine generator 304. The wind-turbine data indicates, for example, the frequency of power output from the wind turbine generator 304, voltage, current, active power, reactive power, power factor, blade pitch angle, rotor rotational speed, operation mode, wind speed, wind direction, hydraulic pressure, temperature, load imposed on predetermined equipment, the presence or absence of abnormalities in various sensors, warnings, other operational statuses, and the like.
Then, the wind farm controller 300 calculates command values (such as a grid-active-power command value cP and a grid-reactive-power command value cQ) for the wind turbine generator 304, with respect to all of the wind turbine generators 304 constituting a wind farm 310, based on the command values sent from the higher-level controller 302 and based on the various data received, and sends the calculated command values to the wind-turbine control systems 308 provided for the respective wind turbine generators 304. Then, each of the wind-turbine control systems 308 controls the controlled wind turbine generator 304 by using a main control device 312 included in the wind-turbine control system 308, based on the received command values.